How Did Two Mothers Both Carry the Same Child?

For what is likely the first time ever, two mothers each got to carry the same child for part of the fetus's development, according to news reports.

The married women, Ashleigh and Bliss Coulter, were each able to carry the developing embryo (and eventually, for one woman, the fetus) thanks to a relatively new fertilization technique, local news station WFAA 8 ABC reported Oct. 25. Ashleigh gave birth to the healthy baby boy, Stetson, five months ago.

So, how did it happen?

The technique — which uses a device called the INVOcell — lies somewhere between in vitro fertilization (IVF) and intrauterine insemination (IUI). During IVF, scientists fertilize eggs with sperm in a lab and then transfer the resulting embryos into a woman's uterus. During IUI, sperm is inserted directly into the uterus, with the goal of making it easier for a sperm cell to reach and fertilize an egg. [Conception Misconceptions: 7 Fertility Myths Debunked]

INVOcell is basically a form of IVF, but instead of the egg being fertilized in a lab, the egg and sperm are put in a small vial that's inserted into a woman’s vagina, along with a diaphragm to ensure it stays in place, according to a 2012 study that outlines the procedure. There, with the help of the body’s heat, the sperm can fertilize the egg. (Essentially, the woman's vagina replaces the incubator in the lab.) After five days, the doctor removes the device to see if an embryo has formed and can then either implant the embryo into the woman's uterus or freeze it for later.

Indeed, the Texas couple's case isn't the first time that the INVOcell technique has been used; it's just the first time it's been used with two women both sharing an embryo. Typically, the technique is used for just one woman. In this case, however, the couple’s doctor took advantage of INVOcell’s unique design to let both mothers in on the pregnancy process.

To explain briefly, after the embryo was incubated in the device in one woman's vagina, the doctor removed the embryo and implanted it into the other woman's uterus, who carried it to term and delivered a healthy baby.

"It's a somewhat novel twist on what we already do" with this technique, said Dr. John Couvaras, the medical director of IVF Phoenix who offers INVOcell at his practice. Couvaras was not involved in the Coulters' case.

Of course, the technique is slightly more complicated than simply removing the embryo from one woman and implanting it in another. For this to work, the mother receiving the five-day-old embryo — in other words, the woman carrying the child to term — would have to have the appropriate uterine lining and hormone levels for a five-day-old embryo, Couvaras told Live Science. If the whole process is successful, this allows one parent to hold the embryo as it first forms and the other to carry the child until delivery. "It’s kind of a neat trick," Couvaras added. [5 Myths About Fertility Treatments]

This fertilization technique may have a few other benefits, too. For starters, some doctors and clinics think the natural fertilization process has a better chance of generating viable embryos than IVF, though not all data supports this theory. That would mean fewer embryos have to be transferred and that allows for more precise control over how many kids someone has. During IVF, doctors often transfer several lab-fertilized embryos into the uterus to increase the odds of one of the embryos successfully implanting and developing, which often results in multiple births (like twins or triplets). It also means there are fewer leftover embryos to freeze, which dodges an ethical dilemma for some people who are unsure about freezing embryos. INVOcell also costs less than IVF, which can be prohibitively expensive due to incubation and medication costs.

While it might still be best for some couples to try IUI first, INVOcell acts an "accelerator" to ensure that IVF is more successful, Couvaras said. Indeed, given these benefits, Couvaras said he isn't sure why the method isn't more popular.